An example is shown in FIG. 1. A low cost wedge anchor bolt 2 has a screw 4 with a screw-head 4a and a shank 4b. An expandable cage 6 is coaxially disposed around the shank 4b, and the shank 4b has a threaded end for engaging the internal threads of a wedge 8 at the distal end of the shank. An insertion portion 9 of the bolt 2, defined by the shank 4b, cage 6, and wedge 8, is inserted into a drilled hole in the structure to which the anchor bolt is to be anchored.
Turning the screw 4 in one direction, typically clockwise, threads the shank 4b further into the wedge 8, drawing the wedge into the cage 6 and thereby causing the cage to expand. Continuing to turn the screw in the same direction eventually results in the cage 6 being expanded sufficiently tightly against the interior surface(s) of the hole to result in a frictional anchoring of the insertion portion 9 therein.
Low cost wedge anchor bolts like that shown in FIG. 1 can be used to provide fall protection for construction workers constructing buildings formed of concrete walls, floors, or ceilings. For that purpose a piece of “bolt attachment” hardware is provided (not shown in FIG. 2) allowing for a worker's connection with the anchor bolt. Typically, the bolt attachment hardware is a plate having two through-apertures, one through which the screw 4 extends, for capturing and thus securing the bolt attachment hardware behind the screw-head and the wall (or ceiling, or other surface) into which the hole is drilled, and the other for allowing the user to connect with the anchor bolt via a clip known as a “carabiner.” Typically, the worker is wearing a harness and the harness is connected with the bolt attachment hardware via a lanyard having a carabiner at each end, one for connecting to the harness and one for connecting to the bolt attachment hardware.
Low cost wedge anchor bolts used in providing fall protection for construction workers are generally not needed after construction is complete. Moreover, to maintain the low cost, the components of the basic wedge anchor bolt are typically formed of ordinary steel and are thus susceptible to corrosion. So it is often desirable, and it is often otherwise required by local building codes, to remove them after construction is complete, because corrosion of the bolt will weaken the surrounding concrete, thus weakening the structure.
The problem is that the low cost wedge anchor bolt is not easily removable. Once the bolt is tightened, the cage 6 and wedge 8 become, together, stuck in the hole, and there is no mechanism provided for separating them. Thus while turning the screw in the opposite direction allows for withdrawing the screw 4 from the hole, the cage 6 and the wedge 8 will typically remain behind, requiring another drilling step to drill these parts out of the hole so that complete removal of the anchor bolt can be accomplished.
“Expansion” type anchor bolts have been provided in the prior art that are easily removable. Examples are those described in U.S. Pat. Nos. 7,357,363 and 8,353,653. A comparison of these with the anchor bolt 2 shows the “expansion” type to be a species of wedge anchor bolt, but with significant adaptations providing for ease of removability. For example, in the typical expansion type anchor bolt, the cage is formed of one or more spoons suspended by flexible rods or filaments; the wedge is spring-biased to wedge the spoons against the interior surfaces of the hole; a slidable bushing is provided for transmitting a hammering force applied to the bushing to the wedge for knocking the wedge out of its stuck position, placing the bolt in a relaxed configuration in which the bolt becomes loose in the hole; and a means is provided for remotely pulling the wedge relative to the spoons against the spring-bias to allow the bolt to maintain the relaxed configuration as the bolt is pulled out from the hole.
These adaptations have resulted in the cost of expansion type anchor bolts being significantly higher than that of basic, low cost wedge anchor bolts like that shown in FIG. 1, to the extent that, even with the additional drilling step, the low cost wedge type anchor bolt is the least costly alternative.
Accordingly there is a need for a basic wedge anchor bolt, i.e., a wedge anchor bolt that is cost competitive with the bolt 2 shown in FIG. 1, which provides an ease of removability that has heretofore only been available in the relatively expensive “expansion” type anchor bolts.